Lets check RIPE-530:

> Re-allocation must be reflected in the RIPE Database. This re-allocation may be on either a
> permanent or non-permanent basis.

> LIRs that receive a re-allocation from another LIR cannot re-allocate complete or partial blocks of
> the same address space to another LIR within 24 months of receiving the re-allocation.

For temporary transfer we make 2 transfers: 1. from LIR A to LIR B. .... 2. Form LIR B to LIR A (back). While address space may not transfer it on within 24 months, so we can't transfer back earlier than in 2 years.